The present invention relates to a glass plate with a water-repellent film and to a method for producing such glass plate by forming the water-repellent film on a glass substrate.
Recently, isocyanate silane compound has been proposed to be used for forming a single-layered water-repellent film on a substrate or for forming the top layer of a two-layered water-repellent film thereon. For example, Japanese Patent Examined Publication JP-B-2-25990 discloses a method for forming a silicon oxide film on a substrate by treating the substrate surface with a silane isocyanate compound containing Si-NCO bond in the molecule. In this publication, there are cited, as the silane isocyanate compound, silicon-containing compounds represented by formulas of Si(NCO)4, RnSi(NCO)4-n and (RO)nSi(NCO)4-n, where R is a hydrocarbon group which may or may not have a substituent, and n is 1, 2 or 3, and condensates of these silicon-containing compounds. Furthermore, there can be used, as the silane isocyanate compound, a silicon compound or a mixture of at least two silicon compounds. Such silicon compound is prepared by condensation of an inorganic silicic acid or a polysiloxane compound with one of the above silicon-containing compounds. Such silicon compound contains at least two NCO groups which are directly bonded to silicon atom.
Japanese Patent Unexamined Publication JP-A-60-219234 discloses a method for forming a multi-layered film on a substrate. This method comprises steps of (a) applying to the substrate a primer composition containing a multifunctional organic isocyanate compound and an acrylic polyol having a hydroxyl value of from 10 to 200 and a NCO/OH ratio of at least 0.6; (b) curing the primer composition by heating and/or drying of the same; and (c) applying to the cured primer composition layer a coating composition containing an organic silicon compound and/or its hydrolysate(s). The organic silicon compound of the step (c) is represented by a general formula of R1aR2bSi(OR3)4-a-b where each of R1 and R2 is alkyl group, alkenyl group, allyl group, or a hydrocarbon group having halogen group, epoxy group, amino group, mercapto group, methacryloxy group or cyano group, R3 has a carbon atom number of from 1 to 8 and is alkyl group, alkoxyalkyl group, acyl group or phenyl group, and each of xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d is 0 or 1.
JP-A-4-342443 discloses an architectural water-repellent article comprising a substrate, a first layer formed on the substrate, and a second layer formed on the first layer. The first layer is prepared from a particular hydrolyzable silane compound or its partial hydrolysate, and the second layer is prepared from a particular isocyanate silane compound.
Hayashi et al. (1994) Journal of the Ceramic Society of Japan 102 [2] 206-209 discloses a water-repellent film formed on a glass plate. This film has a silica undercoating layer and a water-repellent layer formed thereon. The undercoating layer has a thickness of about 100 nm and is prepared by applying tetraisocyanate silane to the glass plate at room temperature. The water-repellent layer is prepared by applying a fluoroalkyl isocyanate silane (C9F19C2H4Si(NCO)3) solution to the undercoating layer, followed by drying at room temperature.
JP-A-6-184527 discloses a water-repellent article having a water-repellent film of a thickness up to 30 nm. This article is prepared by applying a particular water-repellent agent to a substrate. This agent is prepared by a method comprising sequential steps of (a) diluting one or two of a fluoroalkylsilane compound in an amount of 0-5 parts by weight and a long-chain aliphatic silane compound in an amount of 0-15 parts by weight, with 90-110 parts by weight of a solvent; (b) adding 0.1-5 parts by weight of an acid catalyst to the resultant solution; and (c) adding 0-10 parts by weight of a silicon isocyanate compound to the solution. In this method, there are used at least two of the fluoroalkylsilane, the long-chain aliphatic silane compound and the silicon isocyanate compound.
It is therefore an object of the present invention to provide a water-repellent glass plate having a water-repellent film which is superior in solar resistance, abrasion resistance, chemical resistance, and adhesion to a glass substrate thereof.
According to the present invention, there is provided a water-repellent glass plate comprising (a) a glass substrate; (b) a first film which is formed on the glass substrate and is made of silica; and (c) a water-repellent second film formed on the first film. The water-repellent glass plate is prepared by a method comprising steps of: (1) applying a first coating liquid containing tetraisocyanate silane to the glass substrate, thereby to form thereon a precursory film; and (2) subjecting the precursory film to a drying at room temperature or to a heating treatment, thereby to prepare the first film; and (3) applying a second coating liquid to the first film, thereby to form thereon the second film. The tetraisocyanate silane of the step (1) is curable at room temperature (e.g., 20-25xc2x0 C.). The second coating liquid contains an alkoxysilane having at least one fluorocarbon group substituted for at least one hydrogen atom thereof.
In the invention, the tetraisocyanate silane of the first coating liquid is cured by the step (2). The resultant first film becomes a hard silica film, and its surface becomes high in reactivity due to silanol groups formed thereon. With this high reactivity, the first film becomes superior in adhesion to the second film and to the glass substrate. After the step (3), the alkoxysilane of the second coating liquid reacts moderately, for example, with silanol group (SiOH) of the first film and with water in the air, thereby to form the water-repellent second Mm on the first film. With this reaction, alcohol and water may be produced as by-products. These by-products do not become obstacles to the production of the water-repellent glass plate. In contrast to the present invention, if the second coating liquid contains, in place of the alkoxysilane, an alkoxy-free compound, such as RfSiCl3, RfSi(NCO)3 or RfSi(NH){fraction (3/2)} where Rf is a fluorocarbon group, this alkoxy-free compound reacts abruptly with silanol group of the first film and with water in the air, thereby to generate heat and/or hazardous substances such as HCl, HNCO and NH3. According to the invention, the water-repellent second film on the first film is superior in water repellency, solar resistance, and abrasion resistance, while the first and second films do not damage optical characteristics of the glass substrate. Furthermore, the water-repellent glass plate of the invention can be produced by the above-mentioned simple method, using a simple facility, and can be used as architectural and automotive windows, and other various glass articles.
In the invention, the heat treatment of the step (2) can be conducted at a temperature which is higher than room temperature and is up to 700xc2x0 C., for at least 0.1 min. With this heat treatment, the first film becomes harder, and its surface becomes higher in reactivity. Furthermore, the first film becomes more superior in adhesion to the second film and to the glass substrate and thus contributes to improve the second film in solar resistance and abrasion resistance.
In the invention, the second film may be dried at a temperature of from room temperature to 400xc2x0 C., for at least 0.1 min., after the step (3). With this drying, it becomes possible to further improve adhesion between the first and second films and that between the first film and the glass substrate.